The present invention relates to an ultrasound diagnostic apparatus and a method for generating a Doppler waveform image and particularly to an ultrasound diagnostic apparatus for generating a Doppler waveform image through the pulsed Doppler technique or continuous wave Doppler technique.
Conventionally, an ultrasound diagnostic apparatus using ultrasound images has been in a practical use in the medical field. In general, this type of ultrasound diagnostic apparatus comprises an ultrasound probe having a built-in transducer array and an apparatus body connected to the ultrasound probe. The ultrasound probe transmits an ultrasonic beam toward the inside of a subject's body and receives ultrasonic echoes from the subject, and the apparatus body electrically processes the reception signals to generate a B-mode (brightness mode) image.
In addition, for the purpose of obtaining blood flow information, an approach where a Doppler waveform image is generated through the pulsed Doppler technique or the like and displayed with a B-mode image on a display has been adopted.
Accordingly, an ultrasound diagnostic apparatus that performs Doppler processing together with B-mode processing has been disclosed in JP2003-79625A, for example.
In the pulsed Doppler technique, using a transducer array, transmittance of an ultrasonic pulse toward a subject's body and reception of an ultrasonic echo from the subject are repeated at intervals of the pulse repetition frequency (PRF). A reception signal obtained from the transducer array at each transmission and reception of an ultrasonic wave is subjected to phasing addition and thereafter converted into complex data containing a Doppler component through quadrature detection, and the complex data at sample points obtained in a predetermined time width is Fourier-transformed, whereby a spectral signal is acquired. Fourier transformation is continuously carried out at intervals of a predetermined number of sample points, and a Doppler waveform image representing changes in the flow rate with respect to the time axis is generated based on acquired spectral signals.
However, due to interferences between speckle signals or Doppler signals themselves occurring in transmission and reception of ultrasonic waves, for example, black lines appear in a Doppler waveform image thus generated, leading to deterioration of image quality.
Accordingly, a Doppler waveform image data has been conventionally subjected to smoothing treatment in the time direction and the frequency direction to thereby obscure the black lines.
However, the resolution would deteriorate in the time direction as smoothing treatment is performed, whereas the time resolution would deteriorate if it is attempted to improve the image quality. Reversely, if deterioration of the time resolution is suppressed, the black lines would stand out, deteriorating the image quality. This has been a problem.